The present invention is generally related to an information relay technique, and more specifically, is directed to such a technique capable of being effectively applied to an information network-to-network connecting appliance such as a LAN switch.
In general, various data distribution methods have been used in information communication fields, namely in a so-called “multicast distribution method”, the same data is distributed at the same time-from one host to a plurality of hosts. In this multicast distribution method, a plurality of hosts constitute a specific group. While one multicast packet is employed, the same data is distributed to all of hosts belonging to a specific group. Even in the TCP/IP (Transmission Control Protocol/Internet Protocol) corresponding to the standard protocol used in the Internet, there is provided a co-called “IP multicast” technique using this multicast distribution.
An IP multicast system implies such a system capable of performing a multicast communication by an IP address. In an IP multicast system, a specific IP address called as an IP multicast address is defined every specific group. Since an IP multicast packet is used in which an IP multicast address is employed as a destination IP address, the same data is distributed to all of hosts contained in a specific group. In this case, an “IP multicast” implies that a multicast packet transmitted by a multicast server is relayed to a reception terminal of such a host which announces a member of a multicast by a relay process operation executed in specific groups, without considering structures formed in the specific groups. In accordance with this IP multicast technique, while the same data is distributed to the reception terminals of the plural hosts, the following merit can be achieved. That is, while the data is not transmitted to the respective reception terminals, only one packet is transmitted, so that the data can be distributed to all of the reception terminals provided in the specific groups.
An IP multicast corresponds to a protocol of a third layer (network layer) of an OSI (Open Systems Interconnection) reference model, namely such a protocol capable of realizing a multicast communication between second layer (data link layer) networks.
On the other hand, there is such a VLAN (Virtual Local Area Network) technique capable of virtually constituting a second layer (data link) network which may constitute a reference of an IP multicast data distribution.
In this VLAN technique, when a network structure is added, deleted, and changed, a second layer (data link layer) network can be logically constructed without receiving a limitation of a physical network structure. For example, in a physical structure, while a second layer (data link layer) network is logically constituted by communication apparatuses of hosts which are separately connected to different information relay apparatuses, data can be communicated by way of the second layer (data link layer). This VLAN technique owns the following advantage. That is, while the structure of the second layer (data link layer) is changed, there is no need to change the structure of the physical network.
The VLAN technique corresponds to such a technique capable of constituting a network second is layer (data link layer), and therefore, this VAN technique does not depend upon a third layer (network layer) protocol such as an IP multicast. On the other hand, a third layer protocol such as an IP multicast does not either depend upon a method for constituting a second layer (data link layer) network.
To realize such a VLAN, several methods may be employed. For instance, an IP communication may be carried out among VLANs in a layer-3 VLAN system realized by such a system for allocating an IP subnet in a TCP/IP protocol to VLANS.